Males tend to mature sexually at a younger age and smaller size. When it comes to females it essentially depends on how big you want her to be. I personally would only breed a female BCI at about 1.5m and up. The bigger your female the better the chances are that you could get a bigger litter, healthier babies and your female will more than likely be better off during gestation and after dropping the neonates.

Males can mate at 18 months old however I have seen 3 year old males that did not produce viable sperm leading to many slugs (infertile ova) which can cause a blockage and kill the female. Females do best when they are 4 years and older. If you grow them slowly (1 meal a week for 3 weeks then skip a week and then 3 meals again) they will live for 20 years and breed for most of that time. Females live longer if only bred every second year as well. Dont use one male on more than one female. They are not retics or ball pythons. Try have two males for each female if possible.